FEEDBACKJANUARY 29, 2022Defining boundaries
NASA’s Parker Solar Probe is the first
spacecraft to enter the sun’s atmosphere,
crossing the boundary between interplan-
etary space and solar territory called the
Alfvén critical surface, Lisa Grossman
reported in “NASA probe is the first to
visit the sun” (SN: 1/29/22, p. 10).
The probe’s solar visit allowed
researchers to determine that the
Alfvén critical surface lies about
13 million kilometers above the sun’s
surface, Grossman reported. Reader
Jeff Engel wondered what is consid-
ered the sun’s “surface,” given that
the star is made of plasma and doesn’t
have a distinct, solid surface.
In this context, the sun’s “surface”
refers to its photosphere, from which
most of the sun’s photons are emit-
ted, Grossman says. The photosphere
doesn’t have a solid surface either.
Instead, it consists of a layer of gas
and plasma about a few hundred
kilometers thick.Rising seas
The ice shelf holding Antarctica’s
Thwaites Glacier back from the sea
could collapse within five years, raising
the risk of dramatic sea level rise,
Carolyn Gramling reported in “Ice
shelf could collapse within 5 years”
(SN: 1/29/22, p. 12).
Gramling wrote that if the whole
glacier were to slide into the ocean, it
would raise Earth’s sea levels by
65 centimeters, or more than two feet.
Reader Jim Schmitz wanted to know
if water flowing into low-lying areas
could possibly reduce the potential
sea level rise.
Actual measurements of sea level
rise do and will vary from place to
place around the globe for various
reasons, including expanding seawater,
postglacial rebound, the rotation of
Earth and sinking lands. The estimated
sea level rise of 65 centimeters takes
these factors into account, but none
of them change the big picture,
Gramling says.
As for already low-lying coastal
areas, they won’t be able to dispersethe rising waters; they’ll just become
inundated themselves, Gramling says.
“Melting of a major piece of an ice
sheet will drown out everything else,
pun intended.”Ancient landscapers
Neandertals’ campfires, hunting and other
activities may have helped transform an
area in Europe from forest to open grass-
land around 125,000 years ago, making
the hominids the first known to dram ati-
cally impact their environment, Bruce
Bower reported in “Neandertals shaped
European terrain” (SN: 1/29/22, p. 8).
Reader Morten Lindhard asked
how much of that European landscape
was opened with Neandertal-made
fire, rather than by wild grazing
animals.
Researchers don’t know for
sure the percentage of the landscape
transformed by fire, Bower says. A con-
siderable area of the study site — which
borders what is now a 24-hectare
ancient lake basin and a nearby smaller
basin in Germany — appears to have
changed from forest to grassland.
Extensive evidence suggests that
ancient fires were the primary driver
of this change, Bower says.
Several readers wondered if some
of the Neandertal-made fires that
cleared the forest may have been
spread accidentally.
Scientists currently aren’t able
to distinguish archaeologically
between one or a few large fires that
spread accidentally or many smaller,
controlled campfires, Bower says.
Signs of numerous campfires at the
study site over a period of around
2,000 years suggest the latter. But
there is always some uncertainty
when reconstructing ancient
behavior from archaeological evi-
dence, he says.Correction
President Bill Clinton called the
deciphering of the human genome a
“stunning and humbling achievement”
in 2000, not in 2003, as stated in “Read-
ing our genes” (SN: 2/12/22, p. 22).Join the conversation
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Imagine this
Recent experiments (one shown
below) suggest that a quantum
physics theory based only on “real”
numbers fails to explain the real
world, Emily Conover reported in
“Physics requires imaginary num-
bers” (SN: 1/29/22, p. 14). Twitter
user @DwightWebster45 mused
on the findings: “The closer we
look, the more complexity we find.”http://www.sciencenews.org | March 12, 2022 31JINGYUN FANfeedback.indd 31feedback.indd 31 2/23/22 12:16 PM2/23/22 12:16 PM